The present invention relates to signal processing using matched filters, correlators, convolvers, Fourier analyzers, and particularly to low noise signal processors (filters) having input signal x and output signal y and using feedforward circuits for correcting input and filter errors. The signals x and y, for example, may be the transmitted and received signals in a radar, sonar, communications system, or the input and output of a general (recursive or non-recursive) filter.
My U.S. Pat. No. 4,053,750 discloses a feedforward filter in which the error normally associated with the filter is minimized. In my patent it was assumed that the input signal x was perfect, i.e., signal x had no error (noise), so that the error (noise) at the output of the filter was due exclusively to the error generated by the filter alone. Thus, the feedforward circuit of my patent is particularly effective when used to minimize the filter error when the noise which accompanies input x is of little concern. While the system of my patent will work when input signal is moderately noisy it can do so only up to a certain limit above which the noise increasingly captures the filter. To this extent, the feedforward filter of my patent is limited. The present invention seeks to remedy this situation by providing a feedforward filter which operates when both the input signal x is noisy and the filter itself is a noise source.